1. Field of the Invention
The present invention relates to the application of torque forces to an object engaged by a wrench. More particularly, the present invention relates to the application of angular torque forces to a pipe that is being threadedly engaged to, or disengaged from, another pipe with the use of a hydraulic power tong.
2. Description of the Prior Art
Long strings of joined pipe sections are required for the drilling and completion of oil and gas wells. The pipe string is assembled by screwing together pipe sections, or xe2x80x9cjoints,xe2x80x9d typically 30-40 feet in length to make a long, continuous string of pipe that is lowered into the well as the joints are added. The joints are typically equipped with male xe2x80x9cpinxe2x80x9d threads at one pipe end and female xe2x80x9cboxxe2x80x9d threads at the other pipe end. The string is extended by screwing the pin of the joint being added into the box at the top of the string.
During the early days of the drilling industry, the pipe string was screwed together in a two-step process using a xe2x80x9cspinning ropexe2x80x9d and a wrench called a xe2x80x9crig tong.xe2x80x9d One end of the spinning rope was wrapped around the joint being added to the string, and the opposite end was loosely wrapped around a rotating xe2x80x9ccatheadxe2x80x9d powered by the drilling rig. An operator pulling on the tail end of the rope increased the friction of the wraps around the cathead causing the rope to spool over the cathead, pulling the rope away from the joint. A second operator simultaneously restrained the tail end of the rope wound on the pipe to force the pipe to rotate as the rope pulled toward the cathead, spinning the joint pin into the string box. The final makeup torque was applied to the connection using the rig tong, which was also pulled around the joint by the cathead rope.
Hydraulically powered wrenches, called xe2x80x9cpower tongs,xe2x80x9d were developed to replace the spinning rope and manual rig tongs. Power tongs typically include a tong body that surrounds the pipe to be rotated. The tong body carries a hydraulic motor driving a gear transmission connected to a rotary drive that engages and rotates the pipe. The rotary drive is generally equipped with appropriately sized jaws that are selectively actuated by the tong operator to grip the pipe to force the pipe to rotate with the rotary. The tong body is prevented from rotating around the pipe by attaching a restraint, or xe2x80x9csnub line,xe2x80x9d between the tong and a support structure that is fixed relative to the angular motion of the joint being added to, or removed from, the string. In some cases, the support structure is the pipe string extending into the well, in which case an xe2x80x9cintegral backup tong,xe2x80x9d designed to grip the string to provide the required restraint, is also carried by the power tong body.
The torque generated by the power tong is monitored by measuring the force required to restrain the tong from rotating. If the snub line and the centerline of the tong are at a right angle with respect to each other, the torque applied to the pipe is equal to the measured force times the xe2x80x9ctong armxe2x80x9d length. The tong arm length is the distance between the point of attachment of the snub line (or integral backup tong) to the tong body and the centerline of the engaged pipe. The power of the motor and the gear ratio of the transmission connecting the motor to the rotary determine the maximum torque that can be generated by a conventional rotary power tong.
In a typical application, the hydraulic power tong is used to rotate a pipe joint to screw the threads at one end of the joint into mating threads on another joint. Pipe sections having threads such as employed in many proprietary thread designs may be screwed together with very little initial torque until the shoulders in the thread profiles of the two connections engage. Once shoulder engagement occurs, the torque required to properly secure the connection increases substantially above the torque required to rotate the connection to the point of shoulder engagement. Following engagement of the shoulders, very little additional rotation occurs until the desired torque for the connection is obtained.
Most conventional systems used to automatically operate the tongs employ a control signal that bypasses, or xe2x80x9cdumps,xe2x80x9d the hydraulic fluid pressure acting on the tong motor to disable the tong drive system when a desired torque value is sensed. Usually, the dump signal occurs suddenly while the tong motor is generating a high torque force. The weight and momentum of the typical tong prevent it from reacting instantaneously to the dump signal so that the torque applied to the engaged tubular body will frequently exceed the desired minimum torque value.
Another problem with conventional hydraulic power tongs is that the tongs may not provide sufficient power to release (break out) a connection that is made up to a high torque value. This may occur, for example, because the breakout torque of the connection is greater than its makeup torque. When specifying the type of tong to employ for such an application, it is necessary to specify a tong with a higher torque capacity than that required only to make up the pipe. Generally, the greater the torque required for a given job, the larger and more expensive the tong required to perform the job. A related factor is that the space available on most drilling or workover rigs is limited, and it is desirable to keep the equipment size as small as possible while still maintaining the ability to perform the required work.
U.S. Pat. No. 4,938,109 to Torres et al., assigned to the inventor of the present invention, discloses a hydraulic tong system that includes a power tong equipped with an auxiliary power mechanism that applies a force to the tong body to apply torque to the pipe through the stalled tong motor and transmission. The auxiliary power mechanism is preferably a hydraulic piston-cylinder assembly that can be extended or retracted to apply, and hold, the desired torque to a pipe gripped in the tong rotary.
While the Torres et al. system may be used to increase the maximum rated output of the power tong, it is generally used for applying torque to a connection where the desired optimum torque value is well below the maximum torque that can be applied by the tong motor. In such applications, the system is very effective in precisely applying the desired torque for most pipe connections; however, when the pipe is being made up to very low torque values, such as are required in the connections of fiberglass pipe and some other special pipe connections, the tong""s transmission and motor are sometimes moved in reverse as the auxiliary power mechanism moves the tong body in a direction to increase the torque exerted on the gripped pipe. This typically occurs when the final makeup torque for the pipe is so low that it is necessary to limit the hydraulic pressure driving the motor to a level at which the tong motor stalls at a torque that is too low to resist the reverse forces acting through the transmission.
U.S. Pat. No. 5,161,438 describes a power tong that locks the rotary and the housing to prevent the rotary from turning in reverse as the housing is being pivoted with respect to the rotational axis of the rotary. A bolt (or bolts) is used to inhibit the relative rotation. A piston-cylinder arrangement is used for pivoting the housing. All torque generated in the patented system is transmitted through the main rotary gear of the tong.
An integral pipe brake mounted on a rotary power tong grips the pipe as a hydraulic piston-cylinder assembly applies angular force to the tong body. The torque applied to the pipe by the piston-cylinder assembly exceeds that internally generated by the tong. The brake isolates the main rotary gear and transmission from the externally generated torque and prevents the tong body from rotating relative to the pipe while the piston-cylinder assembly is angularly displacing the tong body.
The pipe brake may be actuated to engage automatically once the piston-cylinder assembly is actuated, or the brake may be manually directed by an operator to engage as required. When employed with integral backup tongs, the system may also be automatically or manually actuated to control the selective gripping, release, and rotation of the pipe as required to make or break a pipe connection.
In one embodiment of the invention used to apply a precise, relatively low value of torque to a connection, a regulator is employed to limit the power generated by the hydraulic tong motor. A piston-cylinder assembly is employed to apply the final torque to the connection. In this application, the regulator is set so that the tong motor can produce just enough torque to rotate the pipe until the shoulders in the mating pin and box are engaged. When the shoulders engage, the tong motor stalls, causing the pipe rotation to stop; the brake is manually or automatically engaged with the pipe; and the hydraulic piston-cylinder is manually or automatically actuated to pull the power tong and brake around the gripped pipe until the desired final torque is applied to the connection. The brake isolates the motor and transmission from the piston-cylinder applied torque and prevents them from turning in reverse as the tong body is pulled around the pipe.
The system of the present invention allows the tong motor to spin up the pipe at a relatively rapid rate until the thread shoulders in the connection engage and stop the rotation. Additional torque is applied until some limited value of torque, well below the minimum torque, is reached. Limiting the initial torque output of the tong motor to a value below the desired torque minimum value is done through the tong drive train. The minimum torque is not exceeded because the torque application is automatically limited to a value that is sufficiently low to prevent the momentum of the tong from reaching the minimum torque value after the hydraulic tong motor power is bypassed. Regulating the hydraulic pressure across the tong motor, rather than dumping the pressure and bypassing the motor, allows the tong to maintain the attained low value of torque on the connection until additional torque is slowly and precisely applied by the operation of the piston-cylinder assembly.
When torque above that capable of being produced by the tong motor alone is required, the brake is set and the hydraulic piston-cylinder is actuated to pull the tong body and the gripped pipe in a direction to increase torque on the pipe. The torque magnitude generated by pulling the tong body with the piston-cylinder assembly is equal to the pulling force of the cylinder multiplied by the effective tong arm length. The hydraulic pressure acting on the effective cross-sectional areas of the cylinder piston and connecting rod determine the pulling force of the cylinder.
For a given value of hydraulic pressure operating both the tong motor and the pulling piston-cylinder assembly, a cylinder with a suitably sized piston and rod is capable of applying a significantly greater torque to the pipe than that which can be applied by a conventional tong motor alone.
The hydraulic pressure employed to power a typical hydraulic power tong is generally in the range of 2,000 to 3,000 psi. Depending upon the tong transmission and motor specifications, these pressures can typically produce output torques that range from 6,000 to 60,000 foot pounds. In smaller tongs, such as those designed to run small tubing sized pipe, the torque output with 2,000 psi hydraulic pressure is approximately 6,000 foot pounds. A hydraulic piston-cylinder assembly having an effective cross-sectional area with as little as four square inches of pressure-responsive area can produce a force of 8,000 lbs. in a 2,000 psi hydraulic system. This same 8,000 lbs. acting on a 2-foot long arm can produce 16,000 foot pounds of torque. Accordingly, it will be appreciated that the use of a piston-cylinder assembly in a relatively low pressure hydraulic system can be employed to generate relatively high torque value in a conventional power tong equipped with the pipe brake of the present invention.
When it is necessary to break out a connection in the pipe with a torque that exceeds the torque capacity of the tong motor, the hydraulic piston-cylinder assembly is actuated with the brake set. The connection is broken by the high torque output of the assembly so that the tong motor torque becomes adequate to rotate the engaged pipe, whereupon the cylinder movement is stopped, the brake is released, and the tong motor is engaged to rotate the pipe completely free of the connection with the string.
The hydraulic pressure system used to power the tong motor may be the same as that employed to activate the piston cylinder assembly. Application of torque through the contraction or expansion action of the piston-cylinder assembly applies a controlled, linear change in the torque, as contrasted with the uncontrolled, rapid change in torque that occurs when torque is applied solely by the tong motor.
In a preferred form of the invention, the integral brake locks the tong body to the pipe to relieve the tong motor and transmission components from the amplified torque forces being exerted by the piston-cylinder assembly.
The method of the present invention permits the use of amplified torque applied by the piston-cylinder assembly to overcome the high breakout torque required to initiate the disengagement of the threaded connection. Once the piston-cylinder assembly has applied sufficient breakout torque, the torque required to continue rotation of the pipe can be applied by the rotary tong to complete disengagement of the connection.
During makeup of a pipe connection, the tong motor rotates the pipe being added to the string and applies as much final, non-rotating torque as may be obtained from the motor. Once the shoulders in the threaded connections engage, rotation of the pipe stops, and the brake is set to fix the tong body relative to the pipe. The piston-cylinder assembly is then actuated to rotate the pipe relative to the string to thereby increase the torque above the maximum output of the tong motor, to a maximum desired value.
When employed for making up or breaking out pipe at torque values above those capable of being generated by the tong motor alone, the pipe may be rotated rapidly by the power tong rotary drive during that part of the makeup or breakout at which the torque required to rotate the pipe is less than the torque rating of the motor. Use of the rotary tong to perform the major portion of the rotation of the pipe increases the speed of engaging or disengaging pipe in the string as compared with using manual tongs, which require repeated wrenching movement to completely make up or break out a connection.